It is known to use liquid colourants to colour plastics material. Typically, this is achieved by accurately dosing liquid colourants into a premixer of plastics forming equipment, such as an injection moulder or an extruder. One example of such a system is described in European patent application No. 99304839.6 (publication no. 0965423) in which a dosing pump draws liquid colourant from vertically displaced collapsible reservoirs and delivers it to a premixer.
Another example of a known system is described in WO03/035346. In this system, liquid colourant material for colouring plastics material prior to a plastics forming process is stored in at least one main reservoir. A dosing pump draws the colourant from the main reservoir and delivers a predetermined amount of colourant. An intermediate reservoir between the main reservoir(s) and the dosing pump inlet temporarily retains colourant material. An evacuation pump in communication with the intermediate reservoir selectively evacuates gas therefrom. The disclosure aims to provide a means of accurate and consistent dosing of colourant material without any entrapped air.